Beam scanning exposure is one known method of refining the spot diameter of a light beam, such as a laser beam, to expose a two-dimensional surface; specifically, a beam scanning device such as a galvano-mirror or a polygonal mirror performs a main scan of the two dimensional surface with a single light beam in one direction while the surface to be exposed moves along a sub-scanning direction that intersects with the main scanning direction. The beam scanning exposure technique requires the beam scanning device to rotate at faster speeds when performing high density exposure of a large surface area in order to minimize the exposure process time, thus leading to concern that the vibrations of the drive source or the beam scanning device itself at that time will adversely affect the optical system.
Multi-beam exposure is another known method of two-dimensional exposure with a light beam; here, a one-dimensional light source array emits a plurality of light beams, and the surface to be exposed moves along a direction intersecting with the arrangement direction of the light source array. Given there is a limit to how narrow the gap may be between light sources in the plurality of light sources, the light source array must be repeatedly shifted along the arrangement direction to expose the space between the light beams, which requires high-precision positioning when shifting the light source array.
In contrast, another method based on the above multi-beam exposure technique performs micro-deflection of the plurality of light beams to expose the space between light beams while keeping the light source array itself stationary (refer to Patent Document 1 below). In the existing technology, the beam scanning device is provided with a light source unit for emitting a plurality of light beams spaced at predetermined intervals in a single direction; a scan unit for scanning a surface exposed to the plurality of light beams; an imaging optical system for forming an image of the light beams emitted from the light source unit onto the surface to be exposed; and a micro-deflection unit for micro-deflecting the plurality of beams all at once to expose the space between the beams in the plurality of light beams. Here, the micro-deflection unit may be an acousto-optical element, an electro-optical element or the like.